They can be used for a lot of different things. I used one to atatch a shifter to the seatpost of a detatchable bike some time back: http://i277.photobucket.com/albums/k.../BMXfolder.jpg

Later on I copyed HGR3inOK`s solution that he used on a Moulton: http://www.flickr.com/photos/77836183@N08/8893498312/ and put the shifter on the handlebar on the two similar red and black bikes.

This is a blury photo of the DIY copy of the Carry Freedom hitch on the same bike:

DIY trailerhitch 2

I`ll try to remember to edit to a better picture.

This is Anton`s fat alu dropouts with the Carry Freedom hitch on a Nexus7 hub and anti rotation washer. Not sure why I did not have the samë problem as the OP (or maybe I did and forgot):

Antons trailerhitch